1. The field of art to which the invention pertains includes pipe joints and pipe couplings, particularly those directed to constructions adapted for effecting electrical continuity between the pipe and coupling elements.
2. The use of couplings for effecting a leak-proof joint with coupled pipe sections is well known. It is likewise known to provide for electrical continuity between coupling elements with the intention of affording cathodic protection to an installed piping system exposed to electrolytic action because of soil conditions or the like. Gasket members employed in such installations typically are of a type exemplified by U.S. Pat. No. 3,259,406 and in the cross referenced application supra. Those gaskets and others similarly adapted are widely used, and each employs some sort of electrically conductive, usually metallic, element which when the gasket is compressed at the joints makes physical and electrical contact between the pipe sections and the adjacent coupling components. Where the pipe had been precoated with a dielectric composition, such gasket devices are effective to penetrate the respective coatings in order to ensure electrical continuity of the system via the uncoated coupling. Typically, couplings of this type are installed under field conditions that frequently represent less than optimum working environments such as at the bottom of a remotely located earth trench. This fact in itself handicaps the installation rendering it most essential that the coupled joint be reliably effective in establishing desired electrical continuity between all affected components without need for elaborate testing procedures to ascertain circuit existence.
A recent trend in the industry has been to extend use of dielectric coatings from the pipe per se to and including all exposed components of the coupling unit or other attached components. Whereas the aforementioned gasket devices continue effective to penetrate the coatings in maintaining electrical continuity between the contained pipe and immediately adjacent components of the coupling, it has been found that with such constructions the coupling bolts and nuts have become electrically isolated from the system. By virtue of their isolation, the bolts and nuts are devoid of the cathodic protection sought to be provided, and as a consequence both have been subject to premature failure constituting the weakest link in the life expectancy of the system.
Because such couplings are normally part of an underground piping system, it has not heretofore been known how to assuredly afford electrical continuity for the bolt and nut without omitting or removing contiguous coating in the vicinity of contact and without elaborate test procedures to ascertain circuit existence. Yet failure to provide protection to the bolts and nuts of the coupling defeats the purpose for which protection was otherwise provided.